Mutations in the THAP1 gene (THAP domain containing, apoptosis-associated protein 1) encoding the transcription factor THAP1 are a cause of adolescent-onset dystonia with mixed phenotype (previously referred to as DYT6). About 100 different mutations have been reported in THAP1, including missense, nonsense, and frameshift mutations.

DYT-THAP1 dystonia usually presents with dysphonia or writer’s cramp in late childhood or adolescence. Over the course of the disease, dystonia spreads to other body parts with prominent craniocervical involvement. As for DYT-TOR1A, the penetrance of DYT-THAP1 is highly reduced (to about 50%) and there is variable expressivity. As in most other dystonia forms, there seems to be no neurodegeneration and no specific disease-related pathology in DYT- THAP1. Also for this form of dystonia, deep brain stimulation should be considered as a therapeutic option despite an overall less favourable and less consistent response